1. Field of the Invention
The present invention relates to an improved apparatus for the thickening by flotation of slurries produced during the treatment, notably by activated slurries, of residual, urban or industrial waters.
2. Background and Relevant Materials
Presently for the thickening of slurries arising from the treatment of residual, urban or industrial waters, one resorts frequently to the flotation technique consisting substantially of introducing into a suspension of the slurry to be thickened a pressurized fluid, generally water into which air under pressure has been introduced and which is expanded so as to cause the formation of fine bubbles which unite themselves to the slurry particles and drive them into an ascending movement, thereby bringing them to the free surface of the liquid from which they are eliminated, generally by scraping.
This technique is implemented in an apparatus, called flotation equipment, which has circular or rectangular shape and includes a scraping system for the discharge of the slurries.
After a certain period of operation of said apparatus and due to the flotation phenomenon, the slurry particles mixed with the air bubbles concentrate and form, at the surface of the apparatus, a floating mattress.
A disagreeable smell which is noxious for the environment is released from this apparatus. Therefore, it is most often necessary to cover this apparatus with a structure which is a function of the shape of the structure and of the type of scraping used.
The solutions generally used for covering the rectangular or circular basins having a peripherally driven scraping equipment are:
the installation of the structure inside a building; an inflatable or rigid cover composed of a synthetic material surrounding the whole of the structure.
With these types of installations, the main mechanical elements are inside the structure which is covering the apparatus and they are therefore subjected to the moist and corrosive atmosphere which rapidly degrades the mechanical equipment.
For circular basins provided with scraping equipment which is driven centrally, the covers used need a driving unit outside the moist and corrosive atmosphere of the apparatus. A hydraulic seal is provided for protecting the driving unit from possible releases of corrosive vapor. For these apparatus, the covers used are generally of the type of plane panels made of reinforced concrete or synthetic material. This solution is therefore complex and costly.